Most rubber compositions, especially rubber compositions suitable for tires, contain multiple polymers and may also contain multiple fillers. However, different types of fillers have different affinities towards different types of polymers. For example, in a rubber composition containing polybutadiene and natural rubber, carbon black is likely to be more concentrated in the polybutadiene phase since carbon black has a higher affinity towards polybutadiene versus natural rubber. This type of filler distribution may impact crack growth resistance in rubber compositions such as tire sidewalls or air springs, as well as rolling resistance and/or wear resistance of rubber compositions such as tire treads. Moreover, the domain size of the different types of polymers may impact the crack growth resistance, rolling resistance and/or wear resistance of the rubber composition. Mixing the different polymers for a longer period of time may not offer desirable filler distribution or a reduced domain size of the different polymers. Moreover, adding mix time is inefficient in regard to processing costs.
Thus, what is needed is a rubber composition that has a more even distribution of filler among the different polymers, and/or smaller domain sizes of the different types of polymers.